1. Field of the Invention
This invention relates to a burnt ceramics composition of matter adapted for use as artificial bone in the fields of dentistry, oral surgery and orthopedics.
2. Description of the Prior Art
In accordance with the development of bio-engineering, implantation of artificial bio-material into the bone tissue of a living body has become popular of late. For instance, a dental implantation technique has been developed wherein in order to supplement the loss of natural teeth by artificial teeth, an implant is implanted or inserted in the endosseous or subperiosteal portion of the jaw as a substitute for a clasp abutment tooth of a cantilevered bridge or an abutment tooth of a fixed bridge. The artificial tooth or teeth thus implanted by the implantation technique is called an implant crown, an implant bridge or an implant denture.
The term "implant" as used herein has two meanings, for example, to denote the "implant (element) itself" and also to denote the act of "inserting the implant (element) into the bone tissue of the living body".
As for the material of an implant, metal is conventionally used, predominantly the molded type (ready-made type) of the blade or screw variety or a casted type adapted individually for the endosseous portion of the jaw. In the selection of the metal it is of great importance to take into consideration the so-called "compatibility" between the implant element and the surrounding tissues and especially the compatibility between the surrounding tissues and the surface of a post portion of the implanted artificial tooth. For this purpose, titanium, cobalt-chromium alloys, tantalum, nickel-chromium alloys, iron-nickel-chromium alloys and the like are used. However, these materials have a common drawback in that they can be easily ionized by saliva, secretions in the mouth, food, body fluid, blood and the like, thereby affecting surrounding bone tissues and soft tissues. For instance, in the case where a cobalt-chromium alloy or titanium is used for an implant and the cells surrounding the implant are not compatible with the alloy or metal, it is an essential defect that the surrounding tissues are not adhesive to the implant.
In consideration of this defect, there has been an attempt to use stable plastic materials or ceramic materials instead of easily ionized metals. However, the plastic materials may deteriorate by depolymerization in the living body so that they are not only useless as an implant but also there is a possibility that they may be a carcinogenic factor seriously affecting the surrounding tissues. On the other hand, ceramics are very stable chemically as well as physically and therefore it is the most suitable material to avoid the above-mentioned defect. However, in an X-ray photograph for postoperative medical treatment, the ceramic implant is transparent to the X-rays making radiographic treatment almost impossible and impairing the observation of the boundaries between the implant and the surrounding tissues. This is a great obstacle in many cases which are concerned with examining the growing conditions of the surrounding tissues with respect to the implant, and which are concerned with inspecting postoperative development such as locating that portion of the implant which is embedded in the jaw bone.